The rise of ‘extreme weather attribution’

Houses collapsed in strange corners in sad water, surrounded by debris and pipes that had not been underground for a long time. Crushed cars were left stranded in what became rivers.

These were the scenes in the regions of Germany and Belgium last July, after mournful rains led to heavy flooding. It left large areas submerged, caused extensive wreckage and left more than 150 dead.

Only a few days later, images were released halfway around the world of water-filled subway stations in the Chinese city of Zhengzhou, which was hit by record rain.

They have formed part of a series of extreme weather events that occurred in rapid succession in mid-2021, and focused minds on the growing threats of climate change. But politicians, news broadcasters and scientists have struggled to articulate exactly how warming has contributed to the disasters.

“The sum of all the events we are witnessing in Germany and the forces with which they all occur suggest… That it has something to do with climate change,” Angela Merkel, the then German chancellor, said in the aftermath of the Flooding.

Flooding and landslide in western Austria last year caused significant damage © JFK / EXPA / AFP / Getty

The media reported that a warmer atmosphere could hold more moisture, making heavy rains more likely – but declined to blame flooding in Europe and China on climate change.

However, one scientist Took kill With a stock phrase used by the BBC, that “linking any single event to global warming is complicated.” Ed Hawkins, a professor of climate science at the University of Reading, said the science had “moved on.” “How about ‘experts say that climate change is already increasing the frequency of extreme weather events, and many single events have been shown to be worse by global warming’ instead?” He suggested.

The thirst for knowledge about how climate change influences natural disasters has encouraged the growth of a fast-developing field of study: extreme weather attribution.

That climate change is changing the weather we experience is not disputed: Last year, the world’s top climate scientists said in a headline for the United Nations report that “unprecedented” weather events would become more common as a result of warming.

The challenge is to understand how the rising temperatures affect individual fires, floods or storms. Scientists say that this means looking at how much more likely an extreme event is made by climate change, and how much more severe.

“The fundamental question at the heart of attribution science is: in the absence of climate change, how would the situation be different?” Says Rupert Stuart-Smith, a research associate in climate science and law at the University of Oxford.

Map animation that shows how the Dixie Wildfire spread.  The fire started in Feather River Canyon near Cresta Dam on July 13 and traveled north-east.  When it was contained, the Dixie Fire burned nearly 3,900 square kilometers, making it the second-largest single fire in California history

Identifying cause and effect requires a lot of brain power – human and computerized. Researchers run computer simulations of the Earth’s climate system to see how often an event would occur in different scenarios. They could include the world with 500 years ago, the world today and the world in, say, 100 years time.

Some models are very “zoomed in” and cover relatively small areas of land. This is useful to understand wildfires, for example, that are strongly influenced by their local weather conditions. Other models are much more “zoomed out”, such as those used to analyze heat waves that affect much larger areas.

The scientists crunch the numbers by looking at how often the extreme event occurred in each scenario modeled, and determining whether climate change made it more likely or severe.

A general view of the northeast flank of the Sugar Fire
California has undergone severe wildfires in recent years; A report warns that extreme weather events will become more common as a result of global warming © Neal Waters / Anadolu Agency / Getty

However, no weather event is caused by climate change alone. Extremes, and how much damage they do, will be the result of many factors, including local weather, such as recent levels of rainfall, and an area’s environment and design – does a riverside town have flood protection, for example?

Understanding how all these things come together is crucial for planning. While heavy rains and crack river banks may be unavoidable, communities can have plans to help minimize the damage.

It’s essential that we teach practical lessons from the extremes, says Tim Palmer, Royal Society research professor of climate physics at Oxford University. “Ultimately, this will have to lead to big decisions about how to rig our infrastructure so that it is more resilient,” he says.

Last year, NATO Secretary General Jens Stoltenberg also said that climate change has clear implications for international security, and that “a lot of military infrastructure will be directly affected by global warming. [and] Standing sea level ”.

As attribution science becomes better, researchers think it could be used in legal cases, to link polluters more directly with climate change and its effects. “There is an increasing recognition in the legal community that evidence of this type is highly relevant for lawsuits,” says Stuart-Smith.

Saúl Luciano Lliuya, a Peruvian farmer, is suing the German energy company RWE for his alleged role in driving climate change, and the impact warming is likely to have on the area. Luciano Lliuya wants RWE to help pay for flood defenses to protect his city from Huaraz, which is at risk from the nearby Palkakocha glacial lake. The ongoing case could have major ramifications. If successful, copycat cases are likely to spring up, says Stuart-Smith, so we could see many more.

Ask questions

  1. Explain what extreme weather attribution is.

  2. How do scientists diagnose whether an event is due to climate change or not?

  3. Examine how climate change is expected to have a significant impact on infrastructure and international security.

  4. With reference to the map, explain why this is an effective method of presenting data to show the spread of a fire.

Alsdair Montait, Gordonstown

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